The invention relates to capacitive position sensors, more particularly the invention relates to capacitive position sensors for detecting the position of an object around a curved path.
Capacitive position sensors are applicable to human interfaces as well as material displacement sensing in conjunction with controls and appliances, mechanisms and machinery, and computing.
Capacitive position sensors in general have recently become increasingly common and accepted in human interfaces and for machine control. In the field of home appliances, it is now quite common to find capacitive touch controls operable through glass or plastic panels. These sensors are increasingly typified by U.S. Pat. No. 6,452,514 which describes a matrix sensor approach employing charge-transfer principles. Electrical appliances, such as TV's, washing machines, and cooking ovens increasingly have capacitive sensor controls for adjusting various parameters, for example volume, time and temperature.
Due to increasing market demand for capacitive touch controls, there is an increased need for lower cost-per-function as well as greater flexibility in usage and configuration. There exists a substantial demand for new human interface technologies which can, at the right price, overcome the technical deficits of electromechanical controls on the one hand, and the cost of touch screens or other exotica on the other.
EP1273851A2 discloses a device for adjusting temperature settings, power settings or other parameters of a cooking apparatus. The device comprises a strip sensor which may be linear, curved or circular and may be a capacitive touch sensor or some other form of touch sensor. A linear display is arranged in parallel to the sensor. The capacitive touch sensor is sensitive to the touch of a finger and the display strip is made up of multiple display segments which illuminate to show the current touch setting as defined by a finger touch on the capacitive touch sensor. A predetermined calibration curve relating to a parameter to be adjusted is mapped onto the strip, the range extending from a minimum value to a maximum value. The minimum value may correspond to an off condition of the domestic appliance. Additional operational modes may be associated with the adjustment strip to ascribe new functions to the sensor strip. These can be selected by touching the display for a certain time. For example, a first additional mode can be entered by touching for 5 seconds, and a second additional mode by touching for 10 seconds. One of the additional operational modes is a zoom mode which provides for fine adjustment of the parameter value. The zoom operational mode can be activated by a contact time of, for example, 10 seconds. In the zoom mode an additional digital display is activated to show the current numerical value of the parameter being adjusted. In the zoom mode, only a fraction (e.g. 10%) of the original adjustment range is mapped onto the adjustment strip so that moving a finger across the full length of the sensor strip from left to right (or right to left) will only increase (decrease) the current setting of the parameter value, thereby providing a finer adjustment. During this fine adjustment, the display strip keeps its original function as a relative indicator of the full range between the minimum and maximum values.
More generally, linear, curved and circular sensor strips for adjusting cooker settings have been known for many years, for example see U.S. Pat. No. 4,121,204 (resistive or capacitive sensor), DE19645907A1 (capacitive sensor), DE19903300A1 (resistive sensor), and EP1602882A1 (optical sensor).
WO2006/133976A1, WO2007/006624A1 and WO2007/023067A1 are more recent examples of work on touch-sensitive control strips for domestic appliances using capacitive sensors. These three patent applications were filed before the priority date of the present application, but first published after the priority date of the present application. In particular, WO2006/133976A1 and WO2007/023067A1 disclose sensors with a zoom function similar to the above-described EP1273851A2 which is used for setting a timer.
WO2006/133976A1 provides an adjustment strip with two operational modes. In the first mode the full parameter value range is mapped across the sensor strip. For example 0 to 99 minutes in a timer function. If a user wishes to set the timer to 30 minutes, he touches the strip approximately one third way along. A parameter value of say 34 minutes is sensed by the capacitive sensor, and displayed to the user on a numeric display. Once the initial value has been set, the effect of touching the sensor field is automatically changed to a second mode in which the parameter value is decreased (or increased) finely from the initially selected value by an amount that depends on the distance moved by the finger along the sensor strip. In the example, the user can then slide his finger from right to left to reduce the time from 34 minutes to the desired 30 minutes, using the display for visual feedback. In this way, the user can initially make a rough selection of the desired parameter value with a point and touch action, and then refine it to the exact value desired by a finger sliding action.
WO2007/023067A1 provides an adjustment strip with two operational modes that switch between mapping the full parameter value range across the sensor strip and a partial range selected to show the sub-range of parameter values between which the parameter is most often set by a user. The example of setting the timer on a cooker is given.
While a zoom function is useful, prior art implementations of the zoom function have limitations regarding the manner in which the transition is effected from the full range mode to the zoom mode. In EP1273851A2, the user is made to wait for a certain time, 10 seconds in the specific example, until the transition occurs. On the other hand, in WO2006/133976A1 the transition automatically occurs as soon as a value from the full range is selected. Neither transition mode is ideal, the former can be frustratingly slow for the user, and the latter automatic transition to fine adjustment is undesirable in the case that the initial touch sets a value that is a considerable way off what is intended by the user.